This invention relates to capacity modulation techniques that provide variable control over the volume of compressed refrigerant.
Scroll compressors are widely used in refrigerant compression applications. A scroll compressor includes a first and a second scroll member each having a base and a generally spiral wrap extending from the base. The two wraps interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other. As the one scroll member orbits the size of the compression chambers decreases toward a central discharge port.
One main advantage from scroll compressors is the high efficiency. Scroll compressors do raise some design challenges, however, including capacity control.
Under some system conditions, the amount of refrigerant which is compressed may be desirably reduced from a maximum volume. Scroll compressors have been proposed wherein an unloader valve is mounted near the start of the suction port to communicate some of the refrigerant away from the compression chambers such that the compressed volume of refrigerant is reduced. This control is typically used when the system associated with the compressor has a less than maximum cooling demand.
To date, most capacity control mechanisms for scroll compressors have provided a limited amount of control over the total variation in the volume of compressed refrigerant.
In a disclosed embodiment of this invention, greater control over the capacity modulation, or the volume of refrigerant being compressed, is achieved by utilizing several sequentially arranged unloader valves. In a disclosed embodiment of this invention, a series of pairs of holes are formed through the base of the non-orbiting scroll member. Valves are associated with each pair of holes. A control for the system can control the valves such that less than all of the valves can be open, or alternatively all valves can be opened. Thus, the control has finer gradiation over the volume of refrigerant being compressed.
As is known, scroll compressors typically have a pair of chambers being moved toward the discharge port. An outer chamber is defined radially outward of the orbiting scroll wrap and an inner chamber is defined radially inward of the orbiting scroll wrap. The pair of holes include a hole associated with each of the inner and outer chambers.
In a further feature of this invention, capacity modulation is increased when a scroll wrap having a so-called xe2x80x9chybridxe2x80x9d geometry is utilized. Preferably, the hybrid geometry is such that the geometry of the scroll wrap differs from an involute of a circle to provide an increased volume of refrigerant adjacent the suction of the scroll compressor. Scroll wraps having such hybrid geometry are known, and the basic geometry of the scroll wrap forms no portion of this invention. However, by utilizing an unloader valve associated with the suction port in a scroll compressor having a hybrid wrap geometry, such that there is increased volume adjacent the suction port, even greater control over the final capacity of the scroll compressor is achieved.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.